As one cause of the global warming phenomenon, the greenhouse effect due to CO2 has been pointed out, and a countermeasure thereof has internationally becoming an urgent business to protect a global environment. The cause of CO2 generation includes all human activity fields in which fossil fuels are combusted, and a demand for suppressing discharge of CO2 has becoming stronger. In accompany with this, with respect to power generating facility such as a thermal power plant in which a large amount of fossil fuels are used, a method, in which a flue gas of a boiler is brought into contact with an amine-based absorbent such as an aqueous amine compound solution to remove and recover CO2 in the flue gas, has been intensively studied.
A method, in which CO2 is removed from the flue gas in an absorptive manner by using the absorbent as described above, CO2 is collected in a desorption manner, and the absorbent is regenerated and is circulated again to a CO2 absorber to be used again, is disclosed (for example, refer to Patent Literature 1).
However, a CO2-containing gas and the absorbent come into counterflow contact, and an amount of oxygen contained in air bubbles, which are trapped in the absorbent, is larger than an amount of dissolved oxygen. Accordingly, a degassing technology of removing oxygen from the absorbent by using, for example, a liquid cyclone and the like has been suggested (for example, Patent Literature 2).